RU2532137C2 - Solar cell, solar cell fabrication method and solar cell module - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of solar cell fabrication includes the phases of creation of pn-transition in a semiconductor substrate, creation of passivating layer on the light receiving surface and/or on the light non-receiving surface of semiconductor substrate and creation of the power take-off electrodes on the light receiving surface and on the light non-receiving surface. The passivating layer is formed by the aluminium oxide film with the width up to 40 nm, and the electrode is formed by burning of conducting paste at 500-900°C within the time from 1 second up to 30 minutes with formation of the baked product, which will penetrate through a passivating layer, forming an electrical contact between the electrode and substrate. As a result of creation of aluminium oxide film with the specified width on the substrate surface it is possible to achieve the excellent characteristics of passivation and excellent electrical contact between silicon and electrode only by burning of the conductor paste, that is a standard technology. Besides the phase of burning, which was necessary to achieve the effects of passivation of aluminium oxide film in the past, can be avoided.

EFFECT: cost minimising.

6 cl, 7 dwg

Description

Technical field

[0001] The present invention relates to a solar cell characterized by high productivity, low cost and high efficiency, a method for manufacturing this solar cell and a solar cell module.

State of the art

[0002] Figure 1 schematically depicts a solar cell with a p-type substrate as one example of a solar cell of the prior art, which are usually mass produced using monocrystalline and polycrystalline silicon substrates. A pn junction 103 is formed in it by diffusing an element of group V, such as phosphorus, into the light-receiving surface of the semiconductor substrate (silicon substrate) 101 in high concentration to form an n-type layer 102. For more efficient light retention on both main surfaces (light-receiving and light-not receiving surfaces) of a p- or n-type silicon substrate, dielectric films 104 and 105, respectively, are formed having a lower refractive index than silicon. In these dielectric films 104 and 105, titanium oxide, silicon nitride, silicon carbide, silicon oxide, tin oxide and the like are widely used. Although the thickness of the dielectric film that provides effective optical confinement (optical confinement) varies with its refractive index, the thickness of the silicon nitride film, for example, is usually about 80-100 nm on the light receiving surface and about 90-300 nm on the back surface.

[0003] Also, electrodes 106 and 107 are formed on the light-receiving surface and the non-light receiving (back) surface to extract photogenerated carriers. Among the methods for forming such electrodes, one method that is widely used from a cost point of view is to mix finely divided metal particles, such as silver or aluminum, with an organic binder, print this metal paste using a stencil or the like, and heat treat the paste to bring it into contact with the substrate. The formation of electrodes is usually preceded by the formation of a dielectric film. Thus, in order for the electrode to establish electrical contact with the silicon substrate, the dielectric film between the electrode and the silicon substrate must be removed. This is achieved by introducing the glass component or additives into the metal paste, so that the metal paste can penetrate through the dielectric films 104, 105, making contact with the silicon substrate, which is known as the ability to "burn through".

[0004] Another important function of dielectric films 104, 105 is to limit carrier recombination on the surface of a silicon substrate. Silicon atoms inside the crystal are in a stable state due to covalent bonds between adjacent atoms. However, on the surface corresponding to the edge of the atomic array, an unstable energy level arises, also called an unsaturated valency or dangling bond, since there is no adjacent atom to be attached. A dangling bond is electrically active enough to capture an electric charge photogenerated inside silicon, as a result of which this charge is quenched, subtracted from the operating characteristics of solar cells. To suppress the loss of performance, the solar cell is subjected to a certain final surface treatment to reduce dangling bonds. Alternatively, the antireflection coating gives electric charges to substantially reduce the concentration of electrons or holes on the surface, thereby limiting the recombination of electrons with holes. In particular, the latter is called "passivation due to the field effect" (from the English. "Field effect passivation"). It is known that silicon nitride and similar films have positive charges and, thus, cause passivation due to the field effect.

[0005] However, it is known that if silicon nitride or a similar film having positive charges is applied to the surface of a p-type silicon substrate, the performance of the solar cell is degraded. A positive charge in the film shifts the energy zone on the p-type silicon surface to an inverse state, and the concentration of electrons or minority carriers on the silicon surface becomes higher. If the electrode is formed on the surface of p-type silicon, then the electrons accumulating on the surface flow to the electrode. Since it is the electrode on the n-type silicon side that extracts electrons from the solar cell, the electrons flowing into the p-type silicon side electrode are lost as a leakage current flowing from the output of the solar cell. For this reason, a silicon oxide film, which is said to have a relatively low positive charge, and an aluminum oxide film having a negative charge are now used to passivate the p-type silicon surface.

The following technical documents are considered to be relevant to the present invention.

LEVEL DOCUMENTS

NON-PATENT DOCUMENTS

[0006] Non-Patent Document 1: S. Dauwe, L. Mittelstadt, A. Metz and R. Hezel, Proc. the 17th European Photovoltaic Solar Energy Conference, p. 339, 2001

Non-Patent Document 2: J. Benik, B. Hoex, M.C.M. van de Sanden, W.M.M. Kessels, O. Schultz and S.W. Glunz, Applied Physics Letters, 92, 253504, 2008

SUMMARY OF THE INVENTION

The problem solved by the invention

[0007] However, the alumina film has poor burning ability during electrode formation compared to silicon nitride film and the like, so that the electrical resistance between the electrode and the silicon substrate can increase, making it difficult to provide satisfactory solar cell characteristics. Then, when the electrode is formed on a silicon substrate having an aluminum oxide film formed on it, this film must be configured with a pattern conforming to the electrode pattern. This pattern configuration is usually performed using photolithography or an acid-resistant substance (resist), or by etching the film with acid. It also includes etching paste printing technology and laser-based patterning technology. These technologies, however, are almost unacceptable for commercial use in terms of cost, since not only the number of steps is increasing, but the materials and equipment used are very expensive.

On the other hand, in order to maximize the passivation function of the alumina film, heat treatment of about 400 ° C is necessary. This further complicates the method of manufacturing a solar cell, becoming an obstacle to reducing costs. In addition, conventional conductive paste hardening pastes hardly burn the alumina film, which leads to an increase in electrical resistance and limitation of the characteristics of the solar cell.

[0008] An object of the present invention, which has been developed in view of the circumstances discussed above, is to provide a solar cell having a good ability to burn an alumina film, high productivity, low cost and high efficiency, a method of manufacturing this solar cell and a solar cell module .

Means of solving the problem

[0009] After intensive research to achieve the above goal, the inventors came to an invention that relates to a solar cell containing a semiconductor substrate having a light receiving surface and a light not receiving surface, a pn junction formed in the semiconductor substrate, a passivating layer located on a light receiving surface and / or a light not receiving surface, and power removal electrodes located on the light receiving surface and the light not receiving surface. As a passivating layer, a layer containing an alumina film having a thickness of up to 40 nm is formed, which provides the ability to burn during electrode formation. Thus, it is possible to obtain a solar cell having satisfactory characteristics.

[0010] More specifically, the present invention provides a solar cell, a method for manufacturing the same, and a solar cell module as defined below.

PARAGRAPH 1:

A solar cell comprising a semiconductor substrate having a light receiving surface and a light not receiving surface, a pn junction formed in the semiconductor substrate, a passivating layer located on the light receiving surface and / or the light not receiving surface, and power removal electrodes located on the light receiving surface and a light-receiving surface, wherein said passivating layer includes an alumina film having a thickness of up to 40 nm.

POINT 2:

The solar cell according to claim 1, wherein said passivating layer is located on a non-light receiving surface of a p-type semiconductor substrate or a light-receiving surface of an n-type semiconductor substrate.

POINT 3:

The solar cell according to claim 1 or 2, wherein said passivating layer includes an alumina film and another dielectric film disposed thereon, the other dielectric film being formed from silicon oxide, titanium oxide, silicon carbide or tin oxide.

ITEM 4:

The solar cell according to any one of claims 1-3, wherein said electrode is a sintered product obtained by firing a conductive paste, and this sintered product penetrates through a passivation layer including an alumina film, making electrical contact between the electrode and the substrate.

ITEM 5:

The solar cell according to paragraph 4, wherein said sintered product contains oxide of one or more elements selected from the group consisting of B, Na, Al, K, Ca, Si, V, Zn, Zr, Cd, Sn, Ba, Ta, Tl, Pb, and Bi.

ITEM 6:

The solar cell according to claim 4 or 5, wherein said alumina film has a built-in negative electric charge, which is increased by the firing step.

ITEM 7:

The solar cell according to any one of paragraphs 4-6, wherein the region of said alumina film, which should be located directly below the electrode, is replaced by penetration of the sintered product, and said alumina film is present in at least part of this region, excluding the region located directly below the electrode.

ITEM 8:

A solar cell module comprising a plurality of electrically connected solar cells according to any one of paragraphs 1-7.

ITEM 9:

A method of manufacturing a solar cell, comprising the steps of forming a pn junction in a semiconductor substrate, forming a passivating layer on a light-receiving surface and / or a light-receiving surface of the semiconductor substrate, and forming power take-off electrodes on the light-receiving surface and the light-not receiving surface, wherein as a passivating layer form an alumina film having a thickness of up to 40 nm.

ITEM 10:

The method according to paragraph 9, wherein the electrode is formed by firing a conductive paste at 500-900 ° C. for 1 second to 30 minutes to form a sintered product that penetrates through the passivation layer, making electrical contact between the electrode and the substrate.

ITEM 11:

The method according to claim 10, wherein said sintered product contains oxide of one or more elements selected from the group consisting of B, Na, Al, K, Ca, Si, V, Zn, Zr, Cd, Sn, Ba, Ta, Tl , Pb and Bi.

ITEM 12:

The method according to claim 10 or 11, wherein said alumina film has a built-in negative electric charge, which is increased by the firing step.

Advantageous Effects of the Invention

[0011] Now that an aluminum oxide film of a specific thickness is formed on the surface of the substrate, in particular the light-receiving surface of the p-type semiconductor substrate or the light-receiving surface of the n-type semiconductor substrate, a satisfactory passivation function and close electrical contact between the substrate and the electrode can can only be obtained using the step of firing a conductive paste, which is a prior art technology. The invention eliminates the annealing step that is necessary in the prior art alumina film in order to induce a passivation effect, and is very effective in reducing costs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a sectional view of an exemplary structure of a prior art solar cell.

Figure 2 is a sectional view of one embodiment of a solar cell according to the invention.

Figure 3 is a sectional view of another embodiment of a solar cell according to the invention.

Figure 4 is a sectional view of another embodiment of a solar cell according to the invention.

5 is a sectional view of yet another embodiment of a solar cell according to the invention.

6 is a graph showing contact resistance versus alumina film thickness.

Fig. 7 is a graph showing an effective carrier life before and after heat treatment.

MODES FOR CARRYING OUT THE INVENTION

[0013] Some embodiments of the solar cell of the invention are described below with reference to the drawings, although the invention is not limited to these embodiments of the solar cell.

Figures 2 and 3 depict embodiments of a solar cell according to the invention. The semiconductor substrate 201 (301) is etched with a concentrated alkaline solution of sodium hydroxide or potassium hydroxide with a concentration of 5-60 wt.%, A mixed acid of hydrofluoric acid and nitric acid or the like to remove damage from sawing on its surface. The semiconductor substrate used here may be any of p- or n-type single crystal silicon substrates, p- or n-type polycrystalline silicon substrates, and p- or n-type thin-film silicon substrates. A single crystal silicon substrate can be prepared using the CZ method or the FZ method. For example, a just-cut p-type single crystal {100} silicon substrate can be used in which high-purity silicon is doped with an element of group III, such as B, Ga or In, to give a resistivity of 0.1-5 Ohm · cm.

[0014] Then, the surface of the substrate (light receiving surface) is formed with microscopic protrusions, known as “texture”. Texturing is an effective way to reduce the reflection of solar cells. The texture can be easily formed by immersion in a hot alkali solution, such as sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrogen carbonate or tetramethylammonium hydroxide (concentration of 1-10 wt.%, Temperature 60-100 ° C), for about 10-30 minutes. Often a predetermined amount of 2-propanol is dissolved in a given solution to speed up the reaction.

[0015] Texturing is followed by washing with an acidic aqueous solution such as hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, or a mixture thereof. From the point of view of cost and properties, it is preferable to wash in hydrochloric acid. To improve purity, washing can be performed by mixing 0.5-5 wt.% Hydrogen peroxide in a solution of hydrochloric acid and heating to 60-90 ° C.

[0016] To form a layer 206 (306) of the field on the back surface (from the English back surface field, BSF) on the substrate, gas-phase diffusion of boron bromide or the like is performed at 900-1000 ° C, forming a p ⁺ layer. The BSF layer can be formed on the entire back surface (indicated by 206 in FIG. 2) or locally in accordance with the pattern of the back surface electrode (indicated by 306 in FIG. 3). In conventional silicon solar cells, the BSF layer should be formed only on the back surface. For this purpose, suitable measures are preferably taken to prevent the formation of a p ⁺ layer on the light-receiving surface, for example, by diffusing on a package of two substrates, or by forming a diffusion barrier, such as silicon nitride, on the light-receiving surface. Since the BSF layer, to which the impurity is diffused in high concentration, has a high carrier concentration, the BSF layer is also effective in reducing the electrical resistance between the back surface electrode 208 (308) and the substrate 201 (301).

[0017] Then, gas-phase diffusion of phosphorus oxychloride is carried out to form an n-type layer 202 (302), determining the pn junction 203 (303). Usually, the pn junction should be formed only on the light-receiving surface. For this purpose, suitable measures are preferably taken to prevent diffusion of phosphorus into the back surface, for example, by diffusing on a stack of two substrates with the sides of the p ⁺ layer joined together or by forming a diffusion barrier, such as silicon nitride, on the back surface. After diffusion, any glass residue on the surface is removed with hydrofluoric acid or the like. In addition to gas-phase diffusion, this step can be performed by another method of coating by centrifugation, spraying or other application of a diffusing agent.

[0018] Then, a dielectric film 204 (304) is formed, which serves as an antireflection film on the surface of the substrate or the light receiving surface. As a dielectric film, for example, silicon nitride is deposited to a thickness of about 50-100 nm. A chemical vapor deposition system (hereinafter abbreviated CVD) is used for precipitation. A mixture of monosilane (SiH ₄ ) and ammonia (NH ₃ ) is often used as a reagent gas. In some cases, nitrogen may be used instead of NH ₃ . The desired refractive index can be achieved by diluting the precipitated particles, adjusting the process pressure and diluting the reactant gas with H ₂ gas. The dielectric film is not limited to a silicon nitride film, and instead a silicon oxide, silicon carbide or titanium oxide film can be used which is formed by heat treatment, deposition of an atomic layer (hereinafter abbreviated ALD) or the like.

[0019] On the other hand, a passivating film or passivating layer 205 (305) is formed on the back surface or p-type silicon surface, including (a) an alumina film 205a (305a). Although the CVD or ALD method is often used to deposit an alumina film, vacuum evaporation or spraying can also be used here. CVD or ALD methods typically use trimethylaluminum (TMA) as a reagent and hydrogen (H ₂ ) or argon (Ar) as a carrier gas. As the oxidizing agent of aluminum, oxygen (O ₂ ), carbon dioxide (CO ₂ ), water (H ₂ O), ozone (O ₃ ) or the like are used. One typical reaction scheme is as follows:

Al (CH ₃ ) ₃ + 1.5H ₂ O → 0.5Al ₂ O ₃ + CH ₄

Film deposition using the CVD method occurs when these molecules are decomposed and deposited on a substrate. This decomposition can be caused thermally at 100-400 ° C by heating the substrate or caused electromagnetically at 100-400 ° C by the application of a high-frequency electric field. A crystalline or amorphous film can be formed having arbitrarily any ratio of aluminum to oxygen.

[0020] The alumina film thus obtained carries a negative electric charge, which is believed to be obtained by the following chemical reaction scheme. Here, for simplicity, reference is made to a reaction in an Al ₂ O ₃ film.

2Al ₂ O ₃ → 3 (AlO _4/2 ) ^1- + Al ³⁺

The film is electrically neutral in general. Since Al ³⁺ combines with oxygen in the alumina film, forming a donor / acceptor pair, with which a positive charge is quenched, this film ultimately carries a negative charge.

It is believed that the negative charge generation mechanism described above is equally applicable to other systems, such as an alumina film deviating from stoichiometry, i.e. Al _1-x O _x , where x is an arbitrary constant, or a mixture of alumina with hydrogen, carbon, nitrogen, or the like. Namely, a negative charge can be generated when a given chemical circuit is between Al and O, at least in part, in a system where Al and O are present together.

[0021] Continuing empirical studies of the film thickness of alumina, the inventors have found that the film thickness should be up to 40 nm, preferably up to 30 nm, and more preferably up to 20 nm. Although the lower limit is not critical, the film thickness is usually at least 1 nm to provide uniform coverage over the entire surface of the substrate.

[0022] In order to further enhance the optical retention effect on the back surface, another dielectric film 205b (305b) can be formed on the alumina film 205a (305a) as an upper layer. For the dielectric film 205b (305b), it is preferable to optically use silicon oxide (SiO, SiO ₂ ), but it is also possible to use titanium oxide (TiO, TiO ₂ ), silicon carbide (SiC), tin oxide (SnO, SnO ₂ , SnO ₃ ) or the like. The dielectric film 205b (305b) on the back surface preferably has a thickness of 50-250 nm, more preferably 100-200 nm. If the film is too thin or thick, the optical retention effect may not be sufficient.

[0023] Then, electrodes 207 and 208 (307 and 308) are respectively formed on the light receiving surface and the light not receiving surface (back surface) of the substrate. The electrodes are formed by printing a conductive paste, usually a silver paste obtained by mixing silver powder and glass frit with an organic binder, on a light-receiving surface and a back surface and firing this paste at a temperature of about 500-900 ° C, preferably about 700-850 ° C. for 1 second to 30 minutes, preferably 3 seconds to 15 minutes. Heat treatment causes an aggressive effect on the passivating film of the conductive paste, usually silver paste, as a result of which the electrode in the form of a sintered product of the conductive paste is fired and penetrates through the passivating film, making electrical contact with the silicon substrate. Note that the firing of the electrodes on the light receiving surface and the back surface can be carried out separately on each surface.

[0024] It is the metal oxide in the conductive paste that provides the conductive paste with the ability to burn a passivating film. The metal oxide used here may be an oxide of one or more elements selected from the group consisting of B, Na, Al, K, Ca, Si, V, Zn, Zr, Cd, Sn, Ba, Ta, Tl, Pb and Bi. In order to make the paste penetrate the alumina film and the possible dielectric film, making good contact with the substrate, glass materials such as B-Pb-O, B-Pb-Zn-O, B-Zn-VO can be used , B-Si-Pb-O, B-Si-Pb-Al-O, B-Si-Bi-Pb-O and B-Si-Zn-O.

[0025] The region of the alumina film to be located directly below the electrode is replaced by penetration of the sintered product, and the alumina film is formed in at least a portion of the region except for the region immediately below the electrode. In order to obtain a satisfactory passivation effect, the alumina film is preferably formed on the entire non-light receiving surface (back surface) and / or the entire light receiving surface except for the region immediately below the electrode, more specifically, on the entire light receiving surface of the p-type silicon substrate or the entire light receiving surface of the n-type silicon substrate.

[0026] Although embodiments of a solar cell using a p-type silicon substrate have been described above, the invention is applicable to a solar cell using an n-type silicon substrate. As shown in Figs. 4 and 5, an n-type silicon substrate 401 (501) is prepared by doping high-purity silicon with an element of group V, such as P, As or Sb, and is usually adjusted to a resistivity of 0.1-5 Ohm · cm. A solar cell on n-type silicon can be manufactured in the same way as a solar cell on p-type silicon, except that it is essential to form a p ⁺ layer 402 (502) to form a pn junction 403 (503). On the other hand, an n ⁺ layer for forming a BSF layer on the back surface can be formed on the entire back surface (indicated by 406 in FIG. 4) or locally in accordance with the back surface electrode pattern (indicated by 506 in FIG. 5).

[0027] The light receiving surface can be passivated by forming an alumina film 405a (505a) on the surface of the p ⁺ layer 402 (502) according to the invention and forming another dielectric film 405b (505b) on it, typically a dielectric film of silicon oxide (SiO, SiO ₂ ), titanium oxide (TiO, TiO ₂ ), silicon carbide (SiC) or tin oxide (SnO, SnO ₂ , SnO ₃ ) as the top layer. On the n layer on the back surface, a dielectric film 404 (504) of silicon nitride, silicon oxide, silicon carbide, titanium oxide or the like is preferably formed. Film formation conditions, including film thickness, and electrode formation conditions 407 and 408 (507 and 508) may be the same as for the p-type silicon substrate.

[0028] A reflector is preferably provided on the back surface of the solar cell to reflect back light transmitted by the substrate. As a reflector, aluminum or silver can be used, which can be formed into a film by vacuum evaporation or the like. An equivalent effect can be achieved without additional processing only by applying a white back sheet to the solar cell module. On the other hand, the reflector may be omitted and electricity may be generated, causing scattered light to fall on the back surface. In addition, electricity can be generated by installing a solar cell so that the back surface can become a side of the light receiving surface.

[0029] According to the invention, the solar cell module is obtained by electrically connecting a plurality of solar cells made as described above.

EXAMPLE

[0030] Experiments, examples, and comparative examples are provided below to further illustrate the invention, although the invention is not limited to these examples.

EXPERIMENT 1

Study of the contact resistance of the electrode

[0031] In order to examine the thickness of the alumina film, a conductive paste commonly used for the ability to burn a silicon oxide film was first used to study its ability to burn an alumina film. The burning ability can be evaluated in terms of the contact resistance between the electrode and the silicon substrate.

Gas-phase diffusion of boron bromide was carried out on a p-type textured silicon wafer with an area of 15 cm square having a thickness of 240 μm, thereby causing the diffusion of boron into it with the formation of a p ⁺ layer. An alumina film was formed on the p ⁺ layer by the ALD method, and a silicon oxide film was formed on it by the plasma CVD method. The thickness of the silicon oxide film was selected so that the total thickness of the aluminum oxide film and the silicon oxide film was 100 nm. Commercially available silver paste with a combing ability with a comb pattern was imprinted on these passivating films and burned in a rapid heat treatment furnace (BTO) at a peak temperature of 800 ° C for 3 seconds. 5 samples were prepared for each set of conditions.

[0032] In order to evaluate the contact resistance by the chain method, ribbon-like samples were cut and measured from a plate 1 cm wide and 5 cm long in 5 places.

6 graphically depicts contact resistance versus alumina film thickness. To combine a silica film and an alumina film, when the alumina film thickness was reduced to about 40 nm, the contact resistance shows a sharp drop, and when the alumina film thickness was reduced to 20 nm or less, the contact resistance reaches a value close to that of silicon oxide films 100 nm thick (alumina film thickness = 0 nm). Judging from these results, an alumina film thickness that provides satisfactory electrical contact should be 40 nm or less, preferably 30 nm or less, and more preferably 20 nm or less.

EXPERIMENT 2

Investigation of the effect of passivation on burning an electrode

[0033] Then, a test was carried out to measure the lifetime of the carriers in order to study the effect of passivation depending on the thickness of the alumina film.

On opposite surfaces of the p-type silicon wafer with an area of 15 cm square, having a thickness of 200 μm, which received a mirror finish by acid etching, aluminum oxide films of various thicknesses were formed by the ALD method. In order to impart thermal hysteresis to the heat treatment by roasting the electrode, each sample was subjected to heat treatment in a BTO furnace at a peak temperature of 800 ° C for 3 seconds.

7 graphically depicts the results of measuring the effective lifetime of the media before and after heat treatment. The effective carrier lifetime is the total carrier lifetime, including carrier lifetime in crystalline bulk silicon and carrier lifetime at the silicon-film alumina interface, expressed in microseconds. In Fig. 7, a broken line with black squares indicates the effective life time of the media before heat treatment, and a broken line with white squares indicates the effective life time of the media after heat treatment.

[0034] For all samples, the phenomenon was observed that the carrier lifetime was increased by heat treatment, and the results indicate that the carrier lifetime is independent of the thickness of the alumina film. Using CV measurement, it was proved that extending the lifetime of carriers by heat treatment can be attributed to an increase in the amount of built-in negative charge in the alumina film by heat treatment. The amount of charge before heat treatment was from 1 × 10 ¹⁰ to 3 × 10 ¹⁰ C · cm ^-2 , while the amount of charge after heat treatment increased to about 3 × 10 ¹² C · cm ^-2 for all samples of different thicknesses. Based on the fact that the passivation effect of the alumina film is independent of its thickness, it is believed that charges inside the film are collected near the interface between the silicon substrate and the alumina film.

[0035] From these results, it is clear that a satisfactory passivation effect is achievable even when the alumina film thickness is reduced to 40 nm or less. It was re-discovered that a high amount of negative charge of the alumina film is fully developed due to a brief heat treatment during electrode firing, and the low-temperature annealing step, which was a problem, may be omitted.

EXAMPLE 1

[0036] One hundred (100) cut-off boron-doped {100} p-type silicon substrates having a thickness of 250 μm and a resistivity of 1 Ohm · cm were treated with a hot concentrated aqueous solution of potassium hydroxide to remove cut damage, immersed in an aqueous solution potassium hydroxide / 2-propanol for texturing and then washed with a mixed solution of hydrochloric acid / hydrogen peroxide. Then, a package of substrates with their light-receiving surfaces docked was thermally treated at 1000 ° C in an atmosphere of boron bromide, forming a p ⁺ layer. Then, a package of substrates with their rear surfaces joined together was thermally treated at 850 ° С in phosphorus oxychloride, forming a pn junction. After diffusion, the glass layer was removed with hydrofluoric acid, and the substrates were washed with deionized water and dried. After these treatments, a silicon-nitride film 100 nm thick was deposited as an antireflection film on the entire light-receiving surface in the plasma CVD system.

[0037] The back side passivating film was formed on half (50 substrates) of the substrates thus treated. A 20 nm thick alumina film was deposited on these 50 substrates on the entire back surface at a substrate temperature of 200 ° C in the ALD system, using TMA as a reagent gas and oxygen as an oxidizing agent. The alumina film obtained as a result of this process was a stoichiometric amorphous Al ₂ O ₃ . Then a silicon oxide film 150 nm thick was deposited in a sputtering system.

Then, Ag paste with a comb-like pattern was applied onto the light-receiving surface and the back surface of all substrates by screen printing and dried. Then, the paste was fired in air at 800 ° C for 3 seconds, as a result of which Ag electrodes penetrated through dielectric films both on the light-receiving surface and on the back surface, forming electrical conductivity with a silicon substrate. An Al film was formed in a vacuum evaporation system with a thickness of 2 μm as a reflector on the back of the solar cell.

COMPARATIVE EXAMPLE 1

[0038] The remaining 50 substrates prepared in Example 1 were processed as in Example 1, except that a 100 nm thick silicon nitride film was deposited on the back surface in the same manner as applied to the light-receiving surface of the substrate in Example 1.

[0039] The solar cell characteristics in Example 1 and Comparative Example 1 were measured using a current-voltage tester using a sunlight simulator with an air mass of 1.5. The results are presented in table 1, showing that the performance of solar cells in example 1 as a practical embodiment of the invention is superior to the performance of solar cells in comparative example 1.

Table 1 Dielectric film on a light receiving surface Closed circuit current, mA / cm ² Open circuit voltage, V Fill factor% Conversion efficiency,% Example 1 Al ₂ O ₃ 20 nm
+
SiO ₂ 150 nm 37.8 0.641 78,4 19.0 Comparative Example 1 SiN 100 nm 36.0 0.636 77.5 17.7

[0041] In Example 1, within the scope of the invention, a satisfactory electrical contact is obtained, even though the thickness of the dielectric film on the back surface is greater than in comparative example 1. In addition, since the leakage current is eliminated due to the absence of an inverted layer, a satisfactory fill factor is obtained. and open-circuit voltage and closed-circuit current are significantly improved.

EXAMPLE 2

[0042] One hundred (100) cut-off phosphorus-doped {100} n-type silicon substrates having a thickness of 250 μm and a resistivity of 1 Ohm · cm were treated with a hot concentrated aqueous solution of potassium hydroxide to remove cut damage, immersed in an aqueous solution potassium hydroxide / 2-propanol for texturing and then washed with a mixed solution of hydrochloric acid / hydrogen peroxide. Then, a packet of substrates with their rear surfaces joined together was thermally treated at 1000 ° С in the atmosphere of boron bromide, forming a pn junction. Then, a package of substrates with their light-receiving surfaces joined together was thermally treated at 850 ° C in an atmosphere of phosphorus oxychloride, forming a BSF layer. After diffusion, the glass layer was removed with hydrofluoric acid, and the substrates were washed with deionized water and dried. After these treatments, a silicon nitride film 100 nm thick was deposited as the dielectric film of the back side on the entire back surface in the plasma CVD system.

[0043] On half (50 substrates) of the substrates thus treated, a passivating film of the light receiving surface was formed. A 20 nm thick alumina film was deposited on these 50 substrates over the entire light receiving surface at a substrate temperature of 200 ° C in the ALD system, using TMA as a reagent gas and oxygen as an oxidizing agent. The alumina film obtained as a result of this process was a stoichiometric amorphous Al ₂ O ₃ . A 50 nm thick titanium oxide film was then deposited by atmospheric CVD.

Then, Ag paste with a comb-like pattern was applied onto the light-receiving surface and the back surface of all substrates by screen printing and dried. Then the paste was fired in air at 800 ° C for 3 seconds, as a result of which the Ag electrodes penetrated through the dielectric films on the light-receiving surface and the back surface, forming electrical conductivity with a silicon substrate. An Al film was formed in a vacuum evaporation system with a thickness of 2 μm as a reflector on the back of the solar cell.

COMPARATIVE EXAMPLE 2

[0044] The remaining 50 substrates prepared in Example 2 were processed as in Example 2, except that a 100 nm thick silicon nitride film was deposited on the light-receiving surface in the same manner as applied to the back surface of the substrate in Example 2.

[0045] The solar cell characteristics in Example 2 and Comparative Example 2 were measured using a current-voltage tester using a sunlight simulator with an air mass of 1.5. The results are presented in table 2, showing that the performance of solar cells in example 2 as a practical embodiment of the invention is superior to the performance of solar cells in comparative example 2.

table 2 Dielectric film on a light receiving surface Closed circuit current, mA / cm ² Open circuit voltage, V Fill factor% Conversion efficiency,% Example 2 Al ₂ O ₃ 20 nm
+
TiO 50 nm 36.5 0.651 78.8 18.7 Reference Example 2 SiN 100 nm 36,2 0.637 78.0 18.0

DESCRIPTION OF REFERENCE NUMBERS

[0047] 101, 201, 301, 401, 501: semiconductor substrate

102, 202, 302: n-type layer

402, 502: p-type layer

103, 203, 303, 403, 503: pn junction

104, 105, 204, 304, 404, 504: dielectric film

205, 305, 405, 505: passivating film

205a, 305a, 405a, 505a: aluminum oxide film

205b, 305b, 405b, 505b: dielectric film

206, 306, 406, 506: back layer field layer (BSF)

106, 207, 307, 407, 507: electrode of the light-receiving surface

107, 208, 308, 408, 508: back electrode.

Claims (6)

1. A method of manufacturing a solar cell comprising the steps of forming a pn junction in a semiconductor substrate, forming a passivating layer on the light-receiving surface and / or the light-receiving surface of the semiconductor substrate, and forming power take-off electrodes on the light-receiving surface and the light-not receiving surface, wherein as a passivation layer to form an aluminum oxide film having a thickness of up to 40 nm, while the electrode is formed by firing a conductive paste at 500-900 ° C for 1 second up to 30 minutes with the formation of a sintered product, which penetrates through the passivation layer, establishing electrical contact between the electrode and the substrate. 2. The method according to claim 1, wherein said sintered product contains oxide of one or more elements selected from the group consisting of B, Na, Al, K, Ca, Si, V, Zn, Zr, Cd, Sn, Ba, Ta, Tl, Pb and Bi. 3. The method according to claim 1, wherein said alumina film has a built-in negative electric charge, which is increased by the firing step. 4. The method according to claim 1, wherein the alumina film has a thickness of up to 20 nm. 5. The method according to claim 1, wherein the conductive paste is a silver paste. 6. The method according to claim 1, wherein on the alumina film as a passivating layer another dielectric film is formed, formed from silicon oxide, titanium oxide, silicon carbide or tin oxide.

Images